Sideboard



FIG. 1 is a left front perspective view of a sideboard showing my new design;

FIG. 2 is a side elevational view, the opposite side being a mirror image thereof;

FIG. 3 is a front elevational view thereof; and,

FIG. 4 is a top view thereof.

The views of the sideboard not shown form no part of the claimed design. The dashed lines represent environmental elements only and form no part of the claimed design. 

The ornamental design for a sideboard, as shown and described. 